MIL-T-68410
removed, shall be placed in intimate contact with one of the beams directly over the support. The specimen shall be held in form contact with the surface of the plastic by applying a small load (3 ounce shot bag) on top of the specimen. The other beam under a similar stress without test specimen shall be employed as control. The examination for crazing shall be made while the plastic is under stress at the end of the 24 hour test period. Stresses shall be calculated from the following beam formula, based on the 2:4 beam ratio:
24L
5
8
4 2 2 2 4 5
8
LOAD
SUPPORT
CLAMPED END
SUPPORT
LOAD
DIMENSIONS IN INCHES
Figure 1. Diagrammatic sketch-head of crazing test apparatus with plastic strips in place.
4.6.7 Water vapor transmission rate (WVTR).
4.67.1 Apparatus.
4.6.7.1.1 Humidity cabinet. The humidity cabinet to be used in this test is standard equipment known as the
General Foods moisture vapor transmission cabinet, or equivalent. It shall provide a relative humidity of 90 to
95 percent at a temperature of 38° +1° C ( 100° +2°F) with no condensation on the test dishes or in the space
in which the test dishes are placed. The circulation over the test dishes shall be negligible.
4.6.7.1.2 Test dishes. The test dishes shall be flat, rigid, flanged rectangular cups formed of brass conforming to ASTM 821 (approximately 24 gage) and shall have the dimensions shown below:
Flange: Outside dimensions: 6 by 2 inches
Inside dimensions (opening): 4 by 1 inch
8ody: Inside dimensions: 4 by 1 by 1-1/2 inches deep
The weight of the test dishes shall not exceed 100 grams.
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